Partial karyotypes from controls 2 and 3 demonstrating the origin of JT1q12 and a model for the origin of 1q12 aberrations. (A) Partial karyotypes of control # 2 demonstrating CN gains of 1q21 and CN losses in RCs. Normal chromosomes 1 (left bracket), RC9(q11) by both SKY (chromosome 1 yellow, chromosome 9 white) and FISH (9q11) (aqua) (middle bracket), and progression of CN aberrations resulting from an additional jump of JT1q12 to the RC12(q11) (SKY, chromosome 12 pink) and FISH (right bracket). CN of 1q21 is 4 with the loss of both 9q and 12q in the RCs. (B) Control 3 shows a chromosome 1 by both G-banding and FISH (left bracket) with a 1q21 CN of 2 resulting from a JT1q12 to the telomere of 1p and an isochromosome 1q (right bracket). (C) Model for the origin of CN gains of 1q21. Characterization of aberrations is identified following hypomethylation of 1q12 pericentromeric heterochromatin. Normal chromosome 1 (A) is depicted with a centromere (black) and FISH probes 1q12 (red) and 1q21 (green) (far left). Transient aberrations include cells with decondensation of the 1q12 region (B), triradials of 1q12 resulting in a CN gain of 1q21 (C), and cells with breakage in the 1q12 (red) pericentromeric heterochromatin (D). Extra copies of the JT1q12 originating from a triradial usually either translocate to the telomeric region of an RC (E) or alternatively to the pericentromeric region of an RC (F). Copies of JT1q12s that do not successfully translocate to an RC (G) result in acentric copies of chromosome 1q21 and are subsequently encapsulated into micronuclei and lost from the cell. FISH hybridizations to metaphase chromosomes are shown in inverse 4,6 diamidino-2-phenylindole to delineate G-banding patterns.